Mix flours, salt and baking soda. Add ground flax and stir all. Then add oil, mineral water and lemon juice. You should get a very thick mixture that you can shape with your hands. Form a disc and place in a baking tray covered with baking paper. Sprinkle with flax seeds and sesame seeds. Put in a preheated oven. Bake for 15 minutes at 220 degrees. Check with a toothpick to make sure it is baked. You can also prepare this mixture previous night. Just add baking soda and lemon juice in the morning.